After the successful release of of 4.3 Jellybean on Sony Xperia Z, ZL, ZR, and Tablet Z, Sony has plan to release 4.4.2 Kitkat for Sony Xpeira Z on May 2014. But if you want to get hand on the leaked Sony 4.4.2 KitKat Firmware 10.5.A.0.227 for the Xperia Z (C6602/C6603) for Unlocked bootloader only than you can follow the tutorial here.
Things to know
Please don’t flash this ROM on other Sony Smartphone. It will brick your phone. It is only for Sony Xpeira Z. Don’t expect everything to work, it is not the final release. Few things might be changed in the final release.
Before you start
Make the backup of your data and your current ROM before you start this tutorial.
You should have the Unlocked bootloader. Don’t even try if you have locked bootloader. Your current ROM should be the Stock ROM from sony(4.3 jellybean) or the ROM based on that because some component of this ROM can contain files from these firmwares.
How to install the leaked Kitkat 4.4.2 ROM for Sony Xperia Z?
Reboot your device into the recovery mode. Or you can always shutdown your phone and Press Power and Volume Up key till it opens the recovery mode.
After you are on the recovery mode, I recommend you Wipe Cache and then you can now flash the ROM’s update.zip. It will take sometime so please be patience. When it is finished please reboot your phone. After the reboot it will start some updating process and after few reboot you will finally see the home screen of your Phone.
Enjoy Folks!!! You are now using Android 4.4.2 Kitkat. It is not the final version and some of the things are expected not to work. If any problem then just post it on the comment. We will try to work on that problem. The one problem was the firmware was lagging a little bit. Any way you can reduce the Lag.
First you have to activate the Developers option. To do that navigate to Settings->About->and Tab Build Number for 7 times. Now go back to Settings and tap of Developers Options. Here disable all the animation and select Force GPU render. After you are done restart your phone. This will reduce the Lag and run a lot smoother.
I will be updating the released Android 4.4.2 Kitkat once it is released, if it is available to download.